Method for generating mechanical energy from sunlight

ABSTRACT

A solar energy powered Stirling duplex cooler is presented which includes a Stirling engine and a Stirling cooler. The Stirling engine drives the Stirling cooler to produce cold temperatures for refrigeration or air conditioning. The Stirling duplex cooler includes a solar concentrator to focus high temperature solar radiation upon the Stirling engine expansion space. The Stirling duplex cooler further includes a thermal storage tank to receive and store heat rejected from the cooler expansion space. This stored heat is used to operate the cooler at night. A flywheel connected operatively to engine and cooler expansion space pistons and a crankshaft connected operatively to engine and cooler compression space pistons actuate the pistons to move a working fluid between the expansion and compression spaces.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Continuation of U.S. application Ser. No.17/336,408, now allowed, having a filing date of Jun. 2, 2021, which isa Continuation of U.S. application Ser. No. 17/192,526, now U.S. Pat.No. 11,098,930 having a filing date of Mar. 4, 2021, which is aContinuation of U.S. application Ser. No. 16/510,161, now U.S. Pat. No.11,035,596, having a filing date of Jul. 12, 2019.

BACKGROUND Technical Field

The present disclosure is directed to a solar energy powered Stirlingduplex cooler integrated with a solar concentrator and thermal storagetank. This system utilizes solar power to drive a Stirling engine whichthen drives a Stirling cooler.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

One type of thermal machine capable of providing space heating andcooling, which can use non-polluting gases such as helium or hydrogen,is the Stirling cycle machine. The Stirling cycle is a closed reversiblethermodynamic cycle which can be implemented as a prime mover when heatis supplied. The output is in the form of mechanical power, as for arefrigerator where mechanical power is supplied and the output iscooling capacity, as for a heat pump in which mechanical power issupplied and the output is in the form of heat (or in a reverse mode,cooling capacity).

The Stirling duplex machine is a Stirling cycle cooler driven by aStirling cycle engine. See W Beale, “Free-Piston Stirling Engines—somemodel Tests and Simulations”, International Automotive EngineeringCongress, Detroit Mich., paper No 690230, Jan. 13-17, 1969; and B.Penswick and I Urieli, “Duplex Stirling Machines” Proceedings of the19th annual Intersociety Energy Conversion Engineering Conference, SanFrancisco Calif. paper No QP 051082-A, August 1984, each incorporatedherein by reference in their entirety). A conventional Stirling machine(whether an engine or a cooler) has two chambers connected by aregenerative heat exchanger. (See G. Walker, J. R. Senft “Free PistonStirling Engines”, Lecture Notes in Engineering Edited by C. A. Brebbiaand S. A. Orszag, Springer-Verlag, New York, 1985; and Alhazmy, M. andPeterson, R. B. “A simple computational model for alpha free-pistonsStirling cooler”, Proceedings of the 33rd IECEC, Colorado Springs,Colo., Aug. 2-6, 1998, Paper No. IECEC-98-282, each incorporated hereinby reference in their entirety). Each working space comprises a pistontrapping a working fluid in a cylinder. Each working space is maintainedat a fixed temperature by exchanging heat with the surroundings. Theworking fluid is either compressed or allowed to expand in each workingspace. The working fluid is displaced continuously between the twospaces by the pistons. Pistons of the working spaces are joined to onemain flywheel by connecting rods/crankshafts mechanism. The workingfluid passing through the regenerator gives up the heat to theregenerator and then takes it back as it moves between the two spaces.(See G Walker, “Cryocoolers: part 1 Fundamentals”, The InternationalCryogenics Monograph series, New York, 1983; William Beale, “StirlingEngines for Developing Countries” in Understanding Stirling EnginesWilliam Beale, Arlington, Va. USA; and U.S. Pat. No. 7,171,811 B1, eachincorporated herein by reference in their entirety).

Stirling duplex machines having integrated engine/cooler systems havebeen previously described. (See DE19953512C1; U.S. Pat. No. 4,996,841;“Regenerator and the Stirling Engine”, by Allan J. Organ, (Wiley; 1edition, Mar. 14, 1997, 624 pages); and U.S. Pat. No. 4,462,212, eachincorporated herein by reference in their entirety).

The present disclosure describes a duplex Stirling cycle machine thatconsists of a solar energy powered Stirling engine and a Stirlingcooler. The solar energy powered engine is used to provide the powerneeded to operate the Stirling cooler. Two additional components are asolar concentrator and a thermal storage tank. The solar concentratorhelps to maximize the power and the storage tank is used to provide atemperature differential which operates the cooler at night.

SUMMARY

In an exemplary embodiment, a Stirling duplex cooler is described. TheStirling duplex cooler comprises a Stirling engine having an engineexpansion space and an engine compression space, a solar concentratorconfigured to direct solar heat to the engine expansion space, aStirling cooler having a cooler expansion space and a cooler compressionspace, and a thermal storage tank operatively connected to draw heatfrom the cooler expansion space. The Stirling engine is operativelyconnected to the Stirling cooler to drive the Stirling cooler. A firstregenerator is connected by first tubing between the engine expansionspace the engine compression space, and second regenerator is connectedby second tubing between the cooler expansion space and the coolercompression space. Each expansion space includes a cylinder and apiston, wherein each piston is operatively connected to rotate aflywheel. Each compression space includes a cylinder and a pistonwherein each piston is operatively connected to the crankshaft forreciprocating motion.

The second exemplary embodiment describes a method for operating aStirling duplex cooler which comprises expanding, by solar heating dueto a solar concentrator, a first working fluid within a Stirling engine,driving a flywheel and a crankshaft operatively connected to theStirling engine and a Stirling cooler. The method comprises cooling, bya thermal storage tank, a second working fluid within a Stirling cooler,and driving the Stirling cooler by the Stirling engine.

In another exemplary embodiment, method for operating a Stirling duplexcooler comprises directing solar energy, by a solar concentrator, onto aStirling engine expansion surface containing a first working fluid;heating the first working fluid by the solar energy, wherein heating thefirst working fluid causes the first working fluid to expand and drive afirst piston within a first cylinder of the engine expansion space inthe direction away from the Stirling engine expansion surface; rotating,by the first piston, a flywheel connected to the first piston in a firstdirection, until the piston pushes the heated first working fluidthrough a first regenerator into an engine compression space; filling asecond cylinder within the engine compression space with the firstworking fluid, wherein filling the second cylinder causes a secondpiston within the second cylinder to translate towards the flywheel andwherein translating the second piston towards the flywheel translates acrankshaft connected to a third piston of a third cylinder of a coolercompression space to push a second working fluid through a secondregenerator into a cooler expansion space and moves a fourth pistonthrough a fourth cylinder of the cooler expansion space towards theflywheel, wherein moving the fourth piston towards the flywheel movesthe flywheel in the first direction.

The third embodiment includes cooling the second working fluid first, bymovement of the second working fluid through the second regenenerator,and secondly, by immersing a heat sink connected the fourth cylinder ina thermal storage tank filled with a water-glycol mixture.

The foregoing general description of the illustrative embodiments andthe following detailed description thereof are merely exemplary aspectsof the teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 illustrates a schematic of a heat powered single Stirlingmachine, according to certain embodiments.

FIG. 2A is an illustration of the Stirling duplex cooler, according tocertain embodiments.

FIG. 2B is an illustration of a solar concentrator, according to certainembodiments.

FIG. 2C is an illustration of a regenerator, according to certainembodiments.

FIG. 3A is an exemplary illustration of a first cycle of the Stirlingduplex cooler, according to certain embodiments.

FIG. 3B is an exemplary illustration of a first cycle of the Stirlingduplex cooler, according to certain embodiments.

FIG. 4A depicts the crankshafts, piston rods and dual flywheel outercrank connections in an expanded view, according to certain embodiments.

FIG. 4B depicts the crankshafts, piston rods and dual flywheelconnections in a side view, according to certain embodiments.

FIG. 4C depicts a facing view of flywheel A, according to certainembodiments.

FIG. 4D depicts the crankshafts, piston rods and dual flywheel innercrank connections in a side view, according to certain embodiments.

FIG. 4E depicts a facing view of flywheel B, according to certainembodiments.

DETAILED DESCRIPTION

In the drawings, like reference numerals designate identical orcorresponding parts throughout the several views. Further, as usedherein, the words “a,” “an” and the like generally carry a meaning of“one or more,” unless stated otherwise. The drawings are generally drawnto scale unless specified otherwise or illustrating schematic structuresor flowcharts.

Furthermore, the terms “approximately,” “approximate,” “about,” andsimilar terms generally refer to ranges that include the identifiedvalue within a margin of 20%, 10%, or preferably 5%, and any valuestherebetween.

Aspects of this disclosure are directed to a Stirling duplex cooler andmethods for operating a Stirling duplex cooler.

A conventional Stirling machine is a closed, reversible, thermodynamiccycle which can be implemented as a prime mover or as a cooler. Forengines, heat is supplied to the cycle to produce mechanical power,while for coolers, mechanical power is supplied and the output iscooling capacity.

The ideal Stirling cycle includes the following three thermodynamicprocesses acting on the working fluid; 1) Isothermal Expansion—theexpansion-space and associated heat exchanger are maintained at aconstant high thermal temperature and the gas undergoes near-isothermalexpansion absorbing heat from the hot source; 2) Constant-Volume (knownas isovolumetric or isochoric) heat-removal, in which the gas is passedthrough the regenerator, where it cools, transferring thermal energy tothe regenerator for use in the next cycle; and 3) IsothermalCompression—the compression space and associated heat exchanger aremaintained at a constant low thermal temperature so the gas undergoesnear-isothermal compression rejecting heat to the cold sink. Thetheoretical thermal efficiency equals that of the hypothetical Carnotcycle, i.e. the highest efficiency attainable by any heat engine.

FIG. 1 is a depiction of a conventional single Stirling engine, showingconnections of an expansion space piston 130 to a flywheel 104, anengine compression space piston 118 to the flywheel and tubing 126connecting a regenerator 122 to cylinders 106 and 110. A heat source 152heats gas (hot gas shown as black dots) in the cylinder 106. In thisexample, the majority of the hot gas in cylinder 106 has transferred tothe compression space cylinder 110. The heat of the hot gas has beencaptured in the regenerator 122. The cooled gas particles (shown aswhite circles) have radiated their remaining heat to the coolersurroundings through heat sink 154. As the gas cools, it contracts,pulling piston 118 to close the compression space of cylinder 110. Theflywheel 104 rotates in a clockwise direction, drawing the piston 130 toopen the cylinder 106. This action forces the cooled gas particles backthrough the regenerator 122, where they are warmed by the stored heat,and into the cylinder 106. The regenerator thus acts as a pre-heater,reducing the amount of heat which must be applied to expand the gasparticles as they move into cylinder 106. The gas particles transferback and forth between cylinder 106 and cylinder 110 turning theflywheel. The rotation of the flywheel can be used to drive a furthermechanical device, such as an engine, or to drive an electricalgenerator.

A Stirling machine needs a temperature differential to operate. In theexample of FIG. 1, heat was supplied by a heater 152. However, Stirlingmachines can operate by temperature differentials such as a cold source,such as ice, at the compression space cylinder and room temperature atthe expansion space cylinder. Stirling engines have been shown tooperate at temperature differentials of one degree Celsius.

In the example of FIG. 1, a non-specified heat source 152 was shown.

The present disclosure describes a duplex Stirling cycle machine thatcomprises two Stirling machines: a solar energy powered Stirling engine260 and a Stirling cooler 262 as shown in FIG. 2A.

In an aspect, the solar energy powered Stirling duplex machine isintegrated with a thermal storage tank 214 and a solar concentrator 202.This system utilizes solar power to drive the Stirling engine 260 whichthen drives the Stirling cooler 262.

The Stirling engine receives heat at its high temperature side, produceswork to drive the cooler and rejects heat to the surroundings at anintermediate temperature. The cooler uses the work generated by theengine both to absorb heat at low temperature from the thermal storagetank and reject heat to the surroundings and into the thermal storagetank.

The system, as shown in FIG. 1, consists of three integrated units:

1) A Stirling duplex (i.e. a Stirling cooler driven by a Stirlingengine)

2) A solar concentrator.

3) Thermal storage tank.

The solar energy powered engine is used to provide the mechanical powerneeded to operate the Stirling cooler. The solar concentrators help tomaximize the applied solar power and the thermal storage tank is used toprovide the temperature differential needed to warm the gas and also tooperate the cooler at night time.

A solar concentrator uses lenses, called Fresnel lenses, which directsunlight towards a specific spot by bending the rays of light andfocusing them. Solar concentrators can be characterized by reflectiveconcentrators such as parabolic reflectors and compound parabolicconcentrator reflectors and also by refractive concentrators such asFresnel lenses and convex lenses. The forms of concentration includelinear concentration such as provided by trough parabolic concentrators,and point concentration such as provided by disk parabolicconcentrators.

The solar concentrator of the present disclosure is preferably aparabolic reflector with a Fresnel surface as shown in FIG. 2B. Theparabolic reflector 202 includes a plurality of Fresnel focusing facets272. The focus of each facet is directed towards a heating area 276 ofthe expansion space 244 of the Stirling engine, in this case cylinder206. The arrangement of Fresnel focusing plates compensates for theposition of the sunlight 270 impinging on the concentrator. Regardlessof the sun's position in the daytime, a section of the Fresnel focusingplates will direct sunlight to heat the expansion area, as shown by thefocused rays 274. Further, light which would otherwise be lost when itreflects from the heat receiving surface (usually, a cylinder end) ofthe expansion space is totally internally reflected by the Fresnelfacets back to the heat receiving surface as shown by ray 278. Thisfocused light heats the heating area 276 of the cylinder 206 to drivethe Stirling engine 260. The cylinder 206 end may be coated with a blackpaint 276 in order to absorb the radiation without reflection.

Alternatively, the solar concentrator may be flat, segmented,hemispherical, or any other type of solar concentrator capable offocusing solar energy upon the expansion area of the Stirling engine.

The solar concentrator 202 focuses the solar radiation on the hot sideof the engine (cylinder 206) and heats up the working fluid in theexpansion space of the engine. Fluid at high temperature and highpressure conditions then moves through the regenerator 222 to thecompression space of the engine. The working fluid expands and expelsheat from the cylinder 210 to the surroundings at T₀. The net positivemechanical power produced during this process drives the cooler.

The integrated Stirling machine exchanges heat at three differenttemperatures. The solar concentrator 202 directs concentrated solarenergy at a high temperature, T_(h), onto the surface of the engineexpansion space of cylinder 206. The system rejects heat to the nearbysurroundings at an intermediate temperature, T₀, in both the enginecompression space and in the (Stirling) cooler compression space 234.Heat is also absorbed from the thermal storage tank to keep the tank ata low temperature, T_(l), in the (Stirling) cooler expansion space 238and to provide a higher temperature differential between the (Stirling)cooler compression space 234 and the (Stirling) cooler expansion space238.

Each Stirling machine, whether heat engine or cooler, has two workingspaces. The hot side of the engine is maintained at high temperature bythe solar concentrator and the cold side of the engine is exposed to thesurroundings. The cold side of the cooler is attached to a storage tankand the hot side of the cooler is exposed to the surroundings. Thetemperature of the surroundings is lower than the hot side of the engineand higher than the cold side of the cooler.

The system has two separate working fluid circuits, one for the engineand another for the cooler. In an engine cycle, the working fluidtransitions between the high-temperature T_(h) maintained by the solarcollector and the intermediate temperature T₀ of the surroundings. Forthe cooler, the working fluid operates between the intermediatetemperature, T₀, of the surroundings and the lowest temperature of thestorage tank at T_(l). The fluid circulating inside the engine cycle maybe of a different type or at a different average operational pressurethan that running in the cooler.

As the two Stirling engines are connected through the operation of theflywheel and crankshaft, the integrated engine/cooler system exchangesheat with three different thermal zones simultaneously. The threethermal zones are high-temperature zone at T_(h) maintained by the solarenergy concentrator 202, intermediate-temperature surroundings at T₀ anda low-temperature zone T_(l) of the thermal storage tank 214. At steadystate, the integrated engine/cooler system produces power to drive thecooler and provides cooling simultaneously. Therefore, no net power isproduced by the system.

In order to for the solar energy powered Stirling engine to drive thecooler, the pistons 218 and 216 are connected to a crankshaft 220 forreciprocating motion. Pistons 230 and 228 are connected to the flywheel204 and drive the crankshaft 220.

To operate as an engine, a Stirling engine needs to absorb heat, expandthe gas, reject waste heat, and then compress or contract the gas. Amain component of a Stirling engine is a regenerator, which is placedbetween a hot and lower temperature spaces.

A regenerator works by storing some of the heat that would otherwisehave to be rejected to the environment in the regenerator until theworking gas flow reverses and the heat can be used in the next cycle.The regenerator in a Stirling engine works as an internal heatexchanger, located between the hot and cold parts of the engine. Theworking fluid flows over it in both directions, storing heat from onecycle to be used in the next cycle. A regenerator is used to recycle theheat within the engine, as opposed to wasting the heat to theatmosphere. This improves overall efficiency and power output.

The regenerator transfers heat between a working fluid and aflow-channel wall of the regenerator. The fluid can be helium or anothergas that has suitable thermodynamic properties and that does not reactchemically with engine components. A typical regenerator is cylindricalin overall shape and includes one or more axial passages containing amatrix, which is an open, thermally conductive structure with many flowpaths and large surface area for transfer of heat to and from theworking fluid. The regenerator has an insulated wall which enables heatstorage in the matrix. During the passage of hot particles, heat istransferred from the hot fluid and is stored in the matrix of theregenerator. In the return path, this heat is regenerated and istransferred to the cold fluid passing through the regenerator.

There are many types of regenerators available. All regenerators used inthe present disclosure have low thermal conductance in the lateral(axial) direction and high thermal conductance in the traverse (radial)direction. Matrices in regenerators can be made of various components,including steel wool, steel felt, stacked screens, packed balls, metalfoils, metallic meshes, metallic sponges, carbon fibers, perforatedpyrolytic graphite stacks, open pore metal foams and parallel plates,and combinations of the foregoing. The matrix materials may be any ofstainless steel, copper, bronze, aluminum and Monel 400, andcombinations of the foregoing. In a non-limiting example, a regenerator(222, 224) used in the present disclosure may be a stainless steelcylinder lined with steel wool. In a further non-limiting example, aregenerator may be constructed of a mesh of closely spaced, thin metalplates. A regenerator 280 is shown in FIG. 2C. (See “Stirling EngineRegenerators—Explained—Regenerators—What They Are and How They Work”,American Stirling Company, https://www.stirlingengine.com/regenerators/,incorporated herein by reference in its entirety). Heated particles attemperature T_(h) in Expansion Space 244 enter into the regenerator 280and give up heat. These particles further give up heat in compressionspace 246 with the aid of a heat sink, until they are at temperature T₁.On the return path, the particles are warmed or pre-heated due to thestored heat in the regenerator.

As shown in FIG. 2A, 4A, the Stirling duplex cooler comprises fourpistons (216, 218, 228, 230) each attached by a connecting rod to apiston operatively connected to a flywheel. As shown in FIG. 4A, theflywheel includes a first flywheel 404A and a second flywheel 404B. Eachpiston moves within a respective cylinder (212, 210, 208, 206). Eachcylinder is connected to one of two regenerators (222, 224).

Pistons (216, 218) of a first Stirling engine are each operativelyconnected to either of crankshaft 220 or crankshaft 222, which areconnected to one of the flywheels 204. The crankshafts are driven by thecompression pistons 216, 218 as shown in FIG. 2A. Flywheel 204 isweighted (not shown) to balance the crankshaft/flywheel combination.

An engine expansion space piston 230 and a cooler expansion space piston228 are operatively connected to flywheel 204 to rotate the flywheel.Each expansion piston is connected by a wrist pin 284 to a piston rod350, 352 as shown in FIG. 3A. The flywheel is rotated 360 degrees by thepush-pull action of the piston rods.

Similarly, each compression space piston (216, 218) is connected to acrank 222, 220 respectively for reciprocal motion. The crankshafts areoperated by the reciprocal motion of the pistons 216 and 218 in theircylinders. As piston 218 moves into cylinder 210, the crank pulls piston216 out of cylinder 212 (towards the right, as shown in FIG. 2A). Thecrankshaft 220 alternately rotates 180 degrees in the clockwisedirection then rotates 180 in the counterclockwise direction to push andpull the compression space pistons within their cylinders.

A first regenerator 222 connects the engine expansion space of cylinder206 with an engine compression space of cylinder 210. A secondregenerator 224 connects the cooler expansion space of cylinder 208 withthe cooler compression space of cylinder 212. Heat sink 240 at thebottom of cylinder 208 protrudes into the reservoir of a thermal storagetank 214. Cool air is output at the cooler expansion space. Heat isabsorbed from the thermal storage tank 315 as shown by arrows and entersthe cooler expansion space.

The cylinders and pistons may be machined from any one of the groupconsisting of aluminum, copper, chrome, iron alloys, cobalt basedsuperalloys, silicon carbide, and silicon nitride. Alloys of iron may beany one of nickel, chromium, cobalt, columbium, molybdenum and tungsten.The expansion and the compression spaces of the cylinders should bethermally conducting materials. It is known that both aluminum andcopper have high coefficients of thermal conductivity. In a non-limitingexample, the cylinders and pistons are made of copper. In anothernon-limiting example, the cylinders and pistons are made of aluminum.All contacting surfaces inside the cylinders and the outer surfaces ofthe pistons are highly polished to reduce drag.

In a non-limiting example, the crankshaft and flywheel are manufacturedby forging or casting ductile iron aluminum or aluminum alloys or toolsteel.

Each piston includes a piston ring. For example, piston ring 331 isshown on piston 330 in FIG. 3A. An inner portion of the cylinder 306comprises a large bore in which the piston ring 331 rides. The pistonsand cylinders are scaled with respect to the size of the Stirling duplexcooler. In a non-limiting example, a piston may have a height of onefourth the cylinder bore length.

The pistons and the cylinders forming the working spaces and theregenerators are the basic mechanical components of a Stirling cyclemachine. The Stirling heat engine section and the Stirling coolersections are each hermetically sealed so that no gas escapes.

The regenerator is constructed of material that readily conducts heatand has a high surface area. When hot gas is transferred to the coolcylinder, it is first driven through the regenerator, where a portion ofthe heat is deposited. When the cool gas is transferred back, this heatis reclaimed; thus the regenerator “pre heats” and “pre cools” theworking gas, dramatically improving efficiency.

In a non-limiting example, helium gas may be the working fluid in theengine and the cooler. The working fluid circulating in the engine sidemay be of a different type or at a different average operationalpressure than that running in the cooler side. The working fluid mayselected from the group consisting of helium, hydrogen, air, ethanol,nitrogen, combinations of air and ethanol, fluorine compoundsexemplified by sulfur hexafluoride, perfluorobutane, perfluoropropane,and octafluorocyclobutanenano-fluids; nano-fluids and combinations ofair, ethanol and ZnO nanoparticles.

In a non-limiting example, a water-glycol solution may be used thethermal storage tank 214. The solution is preferably 40% water to 60%glycol. The thermal storage tank is insulated to retain the heat neededto drive the Stirling cooler. The low temperature, T₁, in the thermalstorage tank is preferably in the range of 0 to 10 degrees C., morepreferably 2 to 8 degrees C., even more preferably 3 to 5 degrees C.,even more preferably about 4 degrees C.

Temperature T₀ is preferably in the range of 10 to 30 degrees C., morepreferably 15 to 25 degrees C., even more preferably 18 to 23 degreesC., even more preferably about 23 degrees C. The high temperature,T_(h), is preferably in the range of 60 to 180 degrees C., morepreferably 80 to 150 degrees C., even more preferably about 120 degreesC. The amount of solar energy in the engine expansion space should becontrolled such that T_(h) is less than the boiling point of the workingfluid. For example, the boiling point of helium is about 270 degrees C.and of hydrogen is about 253 degrees C.

A description of the operation of the Stirling duplex machine is givenbelow.

The operation of the Stirling duplex machine is continuous, but isdescribed with respect to two cycles of operation.

Cycle 1: As shown in FIG. 3A, cylinder 306 is filled with gas. Solarenergy from the concentrator 302 heats the gas in cylinder 306. The gasexpands, pushing piston rod 350 down from point B to point A, rotatingflywheel 304 clockwise. The expanded hot gas (black circles) moves intoregenerator 322, where it gives up its heat, entering cylinder 310. Thecooled gas is represented by white circles. As the gas fills thecylinder 310, piston 318 moves towards the flywheel. The crankshaft 320,connected to piston 318, pushes piston 316 to the left through action ofthe flywheel, forcing gas at temperature T₀ (the ambient temperature)into regenerator 324. At the same time, rotation of the flywheel 304pulls piston 328 upwards from point A to point B (see FIG. 3B), whichcreates a vacuum in the cooler expansion space, drawing gas in 312 attemperature T₀ through regenerator 324, and into cylinder 308. The gasin cylinder 308 further gives up heat due to heat sink 356 connected tothermal storage tank 314, until the gas is at temperature T_(l).Cylinder 308 provides useful cooling for refrigeration, air conditioningor other purposes.

Cycle 2: As shown in FIG. 3B, the gas in 310 cools to temperature T₀,and contracts, pulling piston 318 to the right. Momentum from therotation of the flywheel pulls piston 330 down, creating a vacuum. Gasin 310 is drawn into the regenerator 322 where it picks up heat andreenters cylinder 306. Heating the gas by the solar concentrator 302expands the gas, aiding in moving piston 330 down. Piston 316 moves tothe right, creating a vacuum in cylinder 312 and drawing the cold gas attemperature T_(l) from cylinder 308 into the regenerator 324. Momentumof the flywheel pushes piston 328 down, expelling gas at temperatureT_(l) into regenerator 324, where it picks up heat. Gas in cylinder 312is at temperature T₀.

FIG. 4A to 4E show details of the flywheel. The flywheel 404 is a dualmass flywheel, having wheels 404A and 404B. The flywheels are connectedby a shaft having a bearing C. Crankshaft 420 and piston rod 450 areboth connected to crank 403A on flywheel 404A by respective bearings.Crankshaft 422 and piston rod 452 are both connected to crank 403B offlywheel 404B by respective bearings.

The first embodiment is drawn to a Stirling duplex cooler 200 as shownin FIG. 2A. The Stirling duplex cooler of the first embodiment comprisesa Stirling engine 260 having an engine expansion space 244 and an enginecompression space 246, a solar concentrator 202 configured to directsolar heat to the engine expansion space, a Stirling cooler 262 having acooler expansion space 238 and a cooler compression space 234, and athermal storage tank 262 operatively connected to draw heat from thecooler expansion space 238.

A first regenerator 222 is connected by first tubing 226 betweencylinder 206 of the engine expansion space 244 and cylinder 210 of theengine compression space 246. A second regenerator 224 is connected bysecond tubing between a cylinder 212 of the cooler expansion space 234and a cylinder 208 of the cooler compression space 238.

The Stirling duplex cooler includes at least one type of working fluid.The fluid is at least one of helium and hydrogen. Preferably, theworking fluid in each of the first and second hermetically sealedworking spaces is helium, however, the working fluid in the Stirlingengine may be of a different type or at a different average operationalpressure than the working fluid in the Stirling cooler.

The engine expansion space 244, the engine compression space 246, thefirst tubing 226 and the first regenerator 222 form a first hermeticallysealed working space which contains a first working fluid. The coolerexpansion space 238, the cooler compression space 234, the second tubingand the second regenerator 224 form a second hermetically sealed workingspace which contains a second working fluid. As noted above, the firstand second working fluids may be the same or different.

The solar concentrator 202 directs a concentrated solar energy at a hightemperature, T_(h), on the surface of the engine expansion space of theStirling duplex.

The thermal storage tank 214 absorbs heat from the cooler expansionspace 238 to keep the cooler expansion space at a low temperature,T_(l). The absorption of heat is aided by a heat sink 240 on an outersurface of the cooler expansion space (i.e., the cylinder 208). The heatsink is immersed in the thermal storage tank.

To further cool the first working fluid, an outer surface of the enginecompression space 210 further comprises a heat sink (on the cylinder210, see FIG. 3A).

The Stirling duplex cooler 200 further comprises at least one flywheel204 and at least one crankshaft 220. Each expansion space (244, 238)includes a cylinder (206, 208) and a piston (230, 228), wherein eachpiston is operatively connected to rotate the flywheel 204. Eachcompression space (246, 234) includes a cylinder (210, 212) and a piston(218, 216), wherein each piston is operatively connected to thecrankshaft 220, 222 for reciprocating motion.

The second embodiment describes a method for operating a Stirling duplexcooler as is shown in FIG. 2A, 3A, 3B, 4A-4E. The method comprisesexpanding, by solar heating, a first working fluid within a Stirlingengine 260, wherein the expansion of the first working fluid drives aflywheel 204 and a crankshaft 220 connected to the Stirling engine and aStirling cooler 262. The method comprises cooling, by a thermal storagetank 214, a second working fluid within a Stirling cooler 262, anddriving the Stirling cooler by the Stirling engine.

The method for operating a Stirling duplex cooler further comprisesrotating, by the expansion of the first working fluid, the flywheel 204by a piston 230 connected to an expansion space 244 of the Stirlingengine 260; forcing, by momentum of the flywheel, the first workingfluid from the expansion space 244 through a first regenerator 222 andinto a compression space 246 of the Stirling engine, cooling, by thefirst regenerator 222, the first working fluid and further cooling, by aheat sink 354 connected to the compression space of the Stirling engine,the first working fluid.

The method includes translating towards the flywheel, by contraction dueto the cooling of the first working fluid, a crankshaft 220 connected toa piston 218 in the compression space of the Stirling engine.

Driving the Stirling cooler 262 comprises translating, by the crankshaft222, a piston 216 connected to a cooler compression space 234 away fromthe flywheel 204 and driving, by the translation of the coolercompression space piston 216, a second working fluid into a secondregenerator 224. The method continues by cooling the second workingfluid by the second regenerator and drawing the second working fluidinto a cooler expansion space 238 by driving a piston 228 in the coolerexpansion space towards the flywheel, wherein the piston 228 isconnected to the flywheel. The method comprises further cooling thesecond working fluid by rejecting heat into the thermal storage tank 214by means of a heat sink 240 connected to the cooler expansion space 238.

Operating the Stirling duplex cooler includes producing solar heating byfocusing solar radiation by means of a solar concentrator 202.Night-time operation, when there is no solar heating, is ensured by thetemperature differential provided at night duplex cooler by using heatstored in the thermal storage tank 214.

The third embodiment is described with respect to FIG. 2A, 3A, 3B,4A-4E. The third embodiment is drawn to a method for operating aStirling duplex cooler 200 which comprises directing solar energy, by asolar concentrator 202, onto a Stirling engine expansion surface 244containing a first working fluid, heating the first working fluid by thesolar energy, wherein heating the first working fluid causes the firstworking fluid to expand and drive a first piston 230 within a firstcylinder 206 of the engine expansion space in the direction away fromthe Stirling engine expansion surface. Operation comprises rotating, bythe first piston, a flywheel 204 connected to the first piston in afirst direction (shown by arrow, FIG. 2), until the piston 230 pushesthe heated first working fluid through a first regenerator 222 into anengine compression space 246, wherein the first regenerator removes heatfrom the first working fluid. The method continues by filling a secondcylinder 210 within the engine compression space with the first workingfluid, wherein filling the second cylinder causes a second piston 218within the second cylinder to translate towards the flywheel and whereintranslating the second piston towards the flywheel translates acrankshaft 222 connected to a third piston 216 of a third cylinder 212of a cooler compression space 234 to push a second working fluid througha second regenerator 224 into a cooler expansion space 228 and moves afourth piston 228 through a fourth cylinder 208 of the cooler expansionspace towards the flywheel, wherein moving the fourth piston towards theflywheel rotates the flywheel in the first direction.

Further cooling the first working fluid entails removing heat from thefirst working fluid in the engine compression space by means of a firstheat sink 354 connected to the second cylinder 310 until the firstworking fluid contracts and creates a vacuum which moves the secondpiston away from the flywheel.

Further cooling the second working fluid entails removing heat from thesecond working fluid in the cooler expansion space 238 by means of asecond heat sink 240 connected to the fourth cylinder 208, the secondheat sink immersed in a thermal storage tank 214 filled with awater/glycol mixture, until the second working fluid contracts andcreates a vacuum which moves the fourth piston away from the flywheel.

Movement of the crankshaft and flywheel momentum continue rotating theflywheel to move the first piston 330 towards the flywheel, whereinmoving the first piston towards the flywheel creates a vacuum whichdraws the first working fluid through the first regenerator 222 where itis warmed and into the first cylinder. The movement also causes theflywheel move the fourth piston 328 away from the flywheel to force thesecond working fluid through the second regenerator 324 where it iswarmed and into the third cylinder.

Operation of the Stirling duplex cooler includes continuing to move thefirst working fluid in the Stirling engine 260 to drive the secondworking fluid in the Stirling cooler 262 until the second working fluidreaches a temperature T_(l) within the cooler expansion space; and usingthe cooled cylinder as a cooler.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The invention claimed is:
 1. A method for generating mechanical energyfrom sunlight, comprising: directing sunlight, with one or moreparabolic reflective concentrators, onto an outer surface of a firstcylinder of a Stirling engine expansion space containing a first pistonand a first gas; heating the first gas by the solar energy, whereinheating the first gas causes the first gas to expand and drive the firstpiston towards a flywheel operatively connected to the first piston;rotating the flywheel by the first piston in a first direction, untilthe piston pushes the heated first gas through a first regenerator intoa Stirling engine compression space comprising a second cylinder havinga second piston, wherein the first regenerator removes heat from thefirst gas and causes the second piston to translate a crankshaftconnected to the second piston towards the flywheel, wherein translatingthe crankshaft towards the flywheel translates a third piston connectedto the crankshaft into a third cylinder of a Stirling cooler compressionspace to push a second gas through a second regenerator into a Stirlingcooler expansion space and moves a fourth piston through a fourthcylinder of the Stirling cooler expansion space towards the flywheel,wherein moving the fourth piston towards the flywheel rotates theflywheel in the first direction.
 2. The method of claim 1, furthercomprising: removing heat from the first gas in the engine compressionspace by means of a first heat sink connected to the second cylinderuntil the first gas contracts and creates a vacuum which moves thesecond piston away from the flywheel; removing heat from the second gasin the Stirling cooler expansion space by means of a second heat sinkconnected to the fourth cylinder, the second heat sink immersed in athermal storage tank filled with a water/glycol mixture, until thesecond gas contracts and creates a vacuum which moves the fourth pistonaway from the flywheel.
 3. The method of claim 2, further comprisingrotating the flywheel to move the first piston towards the flywheel,wherein moving the first piston towards the flywheel creates a vacuumwhich draws the first gas through the first regenerator where it isheated and into the first cylinder; further rotating the flywheel tomove the fourth piston away from the flywheel to force the second gasthrough the second regenerator where it is heated and into the thirdcylinder; continuing to move the first gas in the Stirling engine todrive the second gas in the Stirling cooler until the second gas reachesa temperature T_(l) within the Stirling cooler expansion space; andusing the cooled cylinder as a refrigeration unit or air conditioner.